Theory of renormalized phonon group velocity in high-temperature superconductors

2019 ◽  
Vol 33 (27) ◽  
pp. 1950337
Author(s):  
Sanjeev K. Verma ◽  
Anushri Gupta ◽  
Anita Kumari ◽  
B. D. Indu
Keyword(s):  
High Temperature ◽  
Group Velocity ◽  
Quantum Dynamics ◽  
Phonon Frequency ◽  
Phonon Dispersion ◽  
High Temperature Superconductors ◽  
Model Calculations ◽  
Phonon Group Velocity ◽  
Frequency Temperature ◽  
Phonon Dispersion Relations

The expressions for the renormalized phonon group velocity (RPGV) has been developed from renormalized phonon dispersion relations obtained with the help of impurity-induced anharmonic quantum dynamics of phonons via Green’s functions. It is observed that RPGV shows dependence on doping, phonon frequency, temperature, and anharmonicity. The [Formula: see text] superconductor has been taken for model calculations to successfully apply the new results of RPGV.

Anisotropy dependence of thec-axis phonon dispersion in the high-temperature superconductors

1998 ◽  
Vol 57 (22) ◽  
pp. 14444-14452 ◽  
Author(s):  
Claus Falter ◽  
Michael Klenner ◽  
Georg A. Hoffmann
Keyword(s):  
High Temperature ◽  
Phonon Dispersion ◽  
High Temperature Superconductors

Cuprate High Temperature Superconductors and the Vision for Room Temperature Superconductivity

SPIN ◽  
2017 ◽  
Vol 07 (02) ◽  
pp. 1750006 ◽  
Author(s):  
Dennis M. Newns ◽  
Glenn J. Martyna ◽  
Chang C. Tsuei
Keyword(s):  
High Temperature ◽  
High Frequency ◽  
Room Temperature ◽  
Phonon Frequency ◽  
High Temperature Superconductors ◽  
Low Frequency ◽  
Unconventional Superconductivity ◽  
Superconducting Transition ◽  
Strongly Coupled ◽  
Room Temperature Superconductivity

Superconducting transition temperatures of 164 K in cuprate high temperature superconductors (HTS) and recently 200 K in H3S under high pressure encourage us to believe that room temperature superconductivity (RTS) might be possible. In considering paths to RTS, we contrast conventional (BCS) SC, such as probably manifested by H3S, with the unconventional superconductivity (SC) in the cuprate HTS family. Turning to SC models, we show that in the presence of one or more van Hove singularities (vHs) near the Fermi level, SC mediated by classical phonons ([Formula: see text]phonon frequency) can occur. The phonon frequency in the standard [Formula: see text] formula is replaced by an electronic cutoff, enabling a much higher [Formula: see text] independent of phonon frequency. The resulting [Formula: see text] and isotope shift plot versus doping strongly resembles that seen experimentally in HTS. A more detailed theory of HTS, which involves mediation by classical phonons, satisfactorily reproduces the chief anomalous features characteristic of these materials. We propose that, while a path to RTS through an H3S-like scenario via strongly-coupled ultra-high frequency phonons is attractive, features perhaps unavailable at ordinary pressures, a route involving SC mediated by classical phonons which can be low frequency may be found.

Superconducting gap anisotropy and d-wave pairing in YBa2Cu3O7−δ

2018 ◽  
Vol 32 (04) ◽  
pp. 1850035 ◽  
Author(s):  
Sanjeev K. Verma ◽  
Anushri Gupta ◽  
Anita Kumari ◽  
B. D. Indu
Keyword(s):  
High Temperature ◽  
Quantum Dynamics ◽  
High Temperature Superconductors ◽  
Nodal Point ◽  
Frequency Dispersion ◽  
Pairing Symmetry ◽  
Superconducting Gap ◽  
Phonon Field ◽  
Many Body Quantum Dynamics ◽  
The Many

Considering Born–Mayer–Huggins potential as a most suitable potential to study the dynamical properties of high-temperature superconductors (HTS), the many-body quantum dynamics to obtain phonon Green’s functions has been developed via a Hamiltonian that incorporates the contributions of harmonic electron and phonon fields, phonon field anharmonicities, defects and electron–phonon interactions without considering BCS structure. This enables one to develop the quasiparticle renormalized frequency dispersion in the representative high-temperature cuprate superconductor YBa2Cu3O[Formula: see text]. The superconducting gap shows substantial changes with increased doping. The in-plane gap study revealed a [Formula: see text]-shape gap with a nodal point along [Formula: see text] direction for optimum doping ([Formula: see text] = 0.16) and the nodal point vanished in underdoped and overdoped regimes. The d[Formula: see text] pairing symmetry is observed at optimum doping with the presence of s or d[Formula: see text] components ([Formula: see text] 3%) in underdoped and overdoped regimes.

Mesoscopic Structures and Their Effects on High-Tc Superconductivity

2017 ◽  
Author(s):  
H. Zhang
Keyword(s):  
High Temperature ◽  
Rock Salt ◽  
High Temperature Superconductors ◽  
Structural Features ◽  
X Ray Diffraction ◽  
Model Calculations ◽  
High Tc ◽  
High Tc Superconductivity ◽  
Electron Phonon Coupling ◽  
Structural Blocks

This article presents the results of model calculations carried out to determine the mesoscopic structural features of high-temperature superconducting (HTS) crystal structures, and especially their characteristic high critical temperature (Tc) and anisotropy. The crystal structure of high-temperature superconductors (HTSc) is unique in having some mesoscopic features. For example, the structures of a majority of cuprite superconductors are comprised of two structural blocks, perovskite and rock salt, stacked along the c-direction. This article calculates the interaction between the perovskite and rock salt blocks in the form of combinative energy in order to elucidate the effects of mesoscopic structures on high-Tc superconductivity. Both X-ray diffraction and Raman spectroscopy show that a ‘fixed triangle’ exists in the samples under investigation. The article also examines the importance of electron–phonon coupling in high-Tc superconductors.

scholarly journals First-Principles Calculation for the Influence of C and O on the Mechanical Properties of γ-TiAl Alloy at High Temperature

Metals ◽  
2019 ◽  
Vol 9 (2) ◽  
pp. 262
Author(s):  
Jiahua Wang ◽  
Yong Lu ◽  
Xiaohong Shao
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
First Principles ◽  
Tial Alloy ◽  
Mechanical Performance ◽  
Phonon Dispersion ◽  
External Pressure ◽  
First Principles Calculation ◽  
Insight Into ◽  
Phonon Dispersion Relations

The elastic constants of temperature dependence, thermal expansion coefficient and phonon dispersion relations of γ-TiAl doped with C/O have been investigated using first-principles calculations in order to gain insight into the mechanical performance of γ-TiAl in cases of high temperature. This study shows that γ-TiAl maintains stability at high temperatures introduced by C or O atoms. Importantly, the hardness increases and retains excellent resistance to external pressure. The results indicate that even if the TiAl alloy is doped with C or O atoms, it can also exhibit excellent mechanical properties at a high temperature.

Lattice dynamical study of face centred tetragonal indium

1983 ◽  
Vol 61 (1) ◽  
pp. 58-66 ◽  
Author(s):  
V. Ramamurthy ◽  
S. B. Rajendraprasad
Keyword(s):  
Frequency Distribution ◽  
Phonon Frequency ◽  
Phonon Dispersion ◽  
Dynamical Study ◽  
Atomic Interactions ◽  
Characteristic Features ◽  
Experimental Values ◽  
First Time ◽  
Good Agreement ◽  
Phonon Dispersion Relations

The phonon dispersion relations and the phonon frequency distribution function of fct indium have been deduced, for the first time, using a lattice dynamical model which expresses the atomic interactions in terms of central, angular, and volume forces. Six elastic constants, four zone boundary frequencies, and an equilibrium condition were used in the evaluation of the force constants. It is shown that this model is elastically consistent and conforms with the translational symmetry of the lattice; the phonon frequencies of indium deduced from it are in very good agreement with the experimental values of Reichardt and Smith and the theoretical values of Garrett and Swihart, but disagree with the theoretical values of Chulkov et al. as well as those of Gunton and Saunders at several wave vectors and polarizations. In addition the phonon frequency distribution curve obtained from this model is in overall agreement with those obtained from the electron tunnelling data, the inelastic scattering of neutrons as well as a pseudopotential model. The apparent characteristic features of these curves, the implications of the crystallographic equivalence between fct and bet lattices, and their relevance in the lattice dynamical study of indium are discussed.

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